Airway traffic control system



0a. 23, 1951 Q S HE D A 2,572,127

AIRWAY TRAFFIC CONTROL SYSTEM Filed Nov. 30, 1944 5 Sheets-Sheet l Bnventors 0162/4 (WM Mm WMM me/f Gttorneg Oct. 23,

Filed Nov. 50, 1944 1951 o. s. FIELD ETAL 2,572,127

' AIRWAY TRAFFIC CONTROL SYSTEM 5 Sheets-Sheet 2 77 Zhwentors W dIfi/a mum/1 63 7/re/r (Ittorneg Oct. 23, 1951 o. s. FIELD ETAL AIRWAY TRAFFIC CONTROL SYSTEM 5 Sheets-Sheet 3 Filed NOV. 50, 1944 m OE lllw- Oct. 23, 1951 o. s. FIELD ET AL AIRWAY TRAFFIC CONTROL SYSTEM 5 Sheets-Sheet 4 Filed Nov. 50, 1944 0. S. FIELD 'ETAL AIRWAY TRAFFIC CONTROL SYSTEM 5 Sheets-Sheet 5 T/Ie/r Gttomeg Oct. 23, 1951 Filed Nov. 30, 1944 Patented Oct. 23, 1951 UNITED STATES PATENT OFFICE 2,572,127 I AIRWAY TRAFFIC CONTROL SYSTEM Oscar S. Field and Sedgwick N. Wight, Rochester, N. Y., assignors to General Railway Signal Company, Rochester, N. Y.

Application November 30, 1944, Serial No. 565,858

Claims. (Cl. 343-11) This invention relates to blind landing and blind route delineation apparatus for aiding pilots of airplanes in landing and in route flying during poor visibility and is an improvement over the prior application of Field, Wight, and Saint, Ser. No. 517,814, filed January 11, 1944, now Patent No. 2,463,094, issued March 1, 1949, and over our prior application, Ser. No. 548,660, filed August 9, 1944, now Patent No. 2,463,095, issued March 1, 1949.

As set forth in the above mentioned prior applications it is desirable for safe flying and landing to have pictorially displayed on a screen before the pilot the locations of ground located radio radiators. This requires suitable space energy transmission which will penetrate fog,

- such as radio energy. In order to display a plurality of such radio radiators at the same time and on the screen of the same cathode-ray tube it is necessary to scan the field of view ahead of the airplane. In accordance with the present invention the swinging of radio beams or focused antennas are to be avoided and the scanning is to be accomplished by triangulation methods involving the difference in radio transmission time over two related paths from a field location to two points on an airplane to indicate the direction of the ground located radio radiator in, say, a horizontal plane and horizontally on the screen, and to employ the time of a radio echo or time of return of a radio triggered impulse to indicate, say, vertically on the screen the distance to such radio reflector or re-radiator.

More specifically, it is proposed to use comparatively short wave length radio energy and to 'so space two receiving antennas on the airplane at right angle and on opposite sides of the same point of the flight axis that the maximum difference in distance from these antennas from aground located radio radiator located anywhere ahead of the airplane cannot be more than a full wave length (one-half plus wave length and one-half minus wave length), so that this difference in distance can be detected by the phase displacement between two received radio currents. In order to measure the distance to such ground located radio radiator it is proposed to render ground located retransmitting apparatus active intermittently and in response to triggering radio energies transmitted from the airplane, to start a sweep of an electron beam in a cathode-ray tube when the triggering radio'radiation leaves the airplane and to plot a fluorescent spot by such beam when 2 the radio energy has been returned to the two antennas and then only when the electron beam scans the screen in a corresponding direction.

Another object of the present invention resides in the provision of means for causing an electron beam to scan a fluorescent screen of a cathode-ray tube radially, such radial scanning preferably extending only through an angle of 180 about a center located at the lower middle part of the screen.

In accordance with another form of the invention it is proposed to ascertain the difference in length of two radio beams directly and irrespective of the frequency used and irrespective of phase relationship.

Other objects, purposes and characteristic features of the invention will be pointed out as the description progresses and will in part be obvious from the accompanying drawing in which:

Fig. 1A illustrates conventionally one embodiment of the invention in which maximum phase displacement between received radio currents is one cycle;

Fig. 13 illustrates the apparatus for one ground location;

Fig. 2 illustrates how the form of the invention of Fig. 1 may be modified, if the frequency of the radio currents is reduced fifty per cent without any change in the spacing of the receiving antennas;

Fig. 3 shows how the speed of the phase shifting portion of the system shown in Fig. 1A may be doubled if two-phase shifting units instead of one are employed;

Fig. 4 modifies Fig. 3 in the same manner as Fig. 2 modifies Fig. 1A;

Fig. 5 illustrates graphically a uniform sawtooth current, how this saw-tooth current may be modulated into two saw-tooth modulated currents displaced in phase and how these currents may be commutated or pole changed to produce the necessary currents to cause semicircular radial scanning of the fluorescent screen;

Fig. 6 shows graphically how phase displacements between 0 and phase displacement may be compared by pole changing one of these circuits each time the phase shifter has shifted through an angle of 180;

Fig. 7 illustrates a phase shifter of the condenser type which may be substituted for the inductive type phase shifter illustrated in Fig. 1A and if this is done the system will function in exactly the same manner as .does the system Figs. 1A and -1B structure-Referring to Fig.

1A of the drawings, the reference character AP designates, by conventionally showing the wings of an airplane, an airplane on the body of which there is located a transmitting antenna TA whereas each of the wings supports a receiving angle of 180, that this energy will cause each of antenna which receiving antennas have been designated RAI and RM. These receiving antennas are preferably supported equal distances from the center line of the airplane and on opposite sides of the same point of this center line. In the forms of invention illustrated in Figs. 1, 3 and 8 these receiving antennas RAI and RA2 are separated a distance of one-half wave length of the radioenergy transmitted by transmitting antenna TA and received by receiving antennas RAI and RA2. In the form of inventions illustrated in Figs. 2 and 4 the frequency of the radio energy employed is presumably half as high so that the wave length of such radio energy is twice that of the former and so that the receiv ing antennas RAI and RA! even though physically spaced the same distance are separated a distance of. one-fourth wave length in the form of invention illustrated in Figs. 2 and 4. I

By referring to Fig. 1A it will be readily seen that if energy is transmitted to the two receiving antennas RAI and RA! from the extreme left of the flight line (90 to the left) that this radio' energy will be received by antenna RAI one-half cycle before it will be received by antenna RA2 but that if energy is transmitted from the lower part of the drawing,-namely, from the extreme right (90 to the right) of the line of flight that this radio energy will reach the antenna RA2 onehalf cycle before it will reach the antenna RAI. In other words, the maximum phase displacement that can exist between radio energies received from a ground location ahead of the airplane by the two antennas RAI and RA! is one whole cycle or 360. That is, the energy received by one antenna may lag as much as 180 behind the energy received by the other antenna and may sometimes lead as much as 180 the energy received by the other antenna so that the maximum phase shift between these two energies that can ever exist is one cycle or 360'.

It is deemed desirable to now briefly discuss the I apparatus located at a particular ground location. This apparatus has been illustrated in Fig. 1B and includes a ground receiving antenna GRA delivering its output energy to a ground receiver GR and which in turn controls or triggers the ground transmitter GT. This apparatus also includes a ground transmitting antenna GTA which is actione or more of the ground transmitters GT to be rendered active and cause the transmission of a radio impulse back toward the airplane from each of such ground stationsthrough the medium of the ground transmitting antenna GTA and it will also be observed that the phase relationship -between the energies picked up by the two airplane carried receiving antennas RAI and RA! from any particular ground station will be displaced in phase dependent upon whether the ground located transmitting antenna is located directly ahead of the airplane, is located toward the right or toward the-left of the center line of the airplane. Although this ground located apparatus has been shown in block form it is readily understood that this apparatus may comprise a simple radi energy repeater including electron tubes], which have their filaments continuously heated so that the transmitting antenna GTA will relay or retransmit an increased quantity of the same character of radio energy that is received by the associated ground receiving antenna GRA.

Referring again to Fig. 1A in accordance with the specific form of the invention illustrated therein the airplane carried transmitter TR does not transmit radi energy continuously through the medium of its antenna TA but transmits intermittent pulses of radio energy each pulse of which consists of a large number of cycles of high frequency radio energy of a wave length com- .mensurate with the spacing of the receiving antennas RAI and RAI. If these receiving antennas RAI and RA2 are, for instance, spaced 10 meters apartthen each wave length will be 20 meters long and the frequency of the radio energy will'be 15 mc. (megacycles). The radio transmitter TR conventionally shown in Fig. 1A includes a suitable electronic tube oscillator which is constructed to generate alternating current of this frequency of, say, 15 me. which transmitter.

is, however. inactive unless rendered active by the pulse generator IG. This pulse generator IG performs two functions. It causes intermittent transmission of radio energy through the medium of the transmitter TR and the transmitting antenna TA and also causes the saw-tooth generator STG to be agitated once for each saw tooth generated and each impulse transmitted, so that the saw-teeth of energy generated by the saw-tooth generator STG are in synchronism withthe pulses of radio energy transmitted by the transmitting antenna TA, there being a short radio pulse transmitted by the transmitting antenna TA at the beginning of each saw-tooth wave energy generated by the saw-tooth generator STG. Y It may be pointed out at this time that this sawtooth energy is used to deflect an electron beam in a cathode-ray tube so that the distance a ground location is from an airplane may be plotted on thescreen of such cathode-ray tube, all asmore fully pointed out hereinafter. It is considered desirable to now describe the cathode-ray tube together with means for sweeping the electron beam thereof by energy derived from the saw-tooth generator STG. V

The cathode-ray tube K is of the usual construction but instead of having been shown of usual conical configuration it hasbeen illustrated as of pyramidal construction. This cathode-ray tubeincludes a fluorescent screen S, of wellknown construction upon which impinges an electron beam EB which beam is emitted by the electron gun including a cathode Ca energized through the medium of a filament energized from and a second anode A2. The first anode also serves as a focusing device to focus the electrons into a comparatively narrow beam as by adjusting the potential applied thereto from the direct current source AB as through the medium of the potentiometer 34. It also includes sweep plates Ill and II for causing a horizontal component of sweeping of the electron beam EB and includes sweep plates l2 and I3 for producing a vertical component of sweep. These sweep plates Ill-ll and |2-|3 are so energized by the saw-tooth energy that the electron beam EB, which is biased by the battery KB to the position 0 on the screen, is scanned radially successively through an angle of 180 after which such scanning performance |s repeated.

To obtain such radial scanning suitable sawtooth energy conversion apparatus is necessary and this apparatus has been illustrated near the top in Fig. 1A and includes a single stationary ring coil and two other ring coils 2| and 22 mounted on a shaft 23 in such manner that the axis of these two coils 2| and 22 are at right angles to each other and are also at right angle to the axis of rotation. This shaft 23 is driven by a motor M operating at a speed dependent upon the number of scans per second of scanning of the cathode-ray screen S that are desired. If it is desired to scan this screen 16 times per second the shaft 23 is rotated at a speed of 8 revolutions per second, there being two scans per revolution, or 480 R. P. M. It will be noted that two-segment commutators are provided. The commutator 25-26 includes commutator segments 25 and 26 suitably supported by the shaft 23 and which segments are connected to the lead-out wires of the rotating coil 2| through the medium of wires a and b. The segments 21 and 28 of the commutator 21-28 are connected to the other rotating co l 22 through the medium of wires 0 and d as illustrated. The commutator 25-26 has associated therewith stationary brushes and 36 whereas the commutator 21-28 has associated therewith stationary brushes 31 and 38. The brushes 35 and 36 are connected to the vertical sweep plates l2 and I3 through wires 32 and 33, whereas the brushes 31 and 38 are connected to the horizontal sweep plates l0 and II through the medium of wires 30 and 3|.

Let us now for a moment refer to Fig. 5 of the drawings to get a more clear understanding of the magnitude of the saw-tooth voltages induced in the rotating coils 2| and 22 of the rotating structure. In Fig. 5 has been illustrated graphically, time being plotted from left to right and potential being plotted vertically, by the graph 40 the saw-tooth energy generated by the sawtooth generator STG. The solid lines of the second graph 4| illustrate the voltage induced in the coil 22 during one complete rotation of the rotor 2|22. It will be observed that at the extreme left of Fig. 5 the voltage graph 4| illustrates saw-tooth voltages of maximum value and that these values fall to zero when this rotor 2|-22 has been rotated one-fourth turn, that they reach a maximum minus value when it has rotate a second quarter of a rotation, that this negative saw-tooth energy then again falls to zero upon completion of a third quarter of rotation and that it again rises to a maximum positive value at the completion of a whole revolution.

Referring now to the voltage graph 42 it will be observed that these saw-tooth voltages are zero when the voltage of graph 4| is maximum and 6 that in all other respects the curves 4| and 42 are alike. It may be pointed out that the beginning ofthe cycle illustrated for both graphs and 42 correspond to the position of the apparatus as illustrated in Fig. 1A at which position the electron beam sweeps up from the point 0 on screen Referring again to the solid lines of graph 42 it will be observed that this graph is exactly the same as the graph 4| (solid lines) except that the graph 42 lags behind the graph 4|.

It should now be remembered that commutators 25-26 and 21-28 have been provided and that the commutator 25-26, which commutates the saw-tooth energy for vertical sweeping, pole changes its leads when the voltage is zero as indicated by the arrows 45 and 46 in Fig. 5 of the drawings, whereas the commutator 21-28 commutates or pole changes the saw-tooth energy when this saw-tooth voltage is a maximum. The effect produced by this commutation by commutators 25-26 and 21-28 and illustrated by dotted lines in graphs 4| and 42, respectively (Fig. 5), results in diflerent kinds of saw-tooth energy modulation. It will be noted that the graph 4| as modified by the dotted lines due to commutation includes only positive voltages and that these sawtooth voltages rise and fall and are always pole changed when they are 0. The saw-tooth voltages for right and left sweep and illustrated by the graph 42 on the other hand start with a zero voltage, build up to a maximum positive voltage, then suddenly reverse to a maximum minus voltage which voltage is then gradually reduced to zero and then builds up in a positive direction until it returns to maximum positive value at which commutation takes place to pole change the leads to cause this maximum positive voltage to be suddenly changed into a maximum minus sawtooth voltage, after which the minus voltages gradually reduce in value until they again reach the zero value upon completion of one revolution of shaft 23. This is as it should be in that if positive voltages are used to sweep the electron beam EB of the cathode-ray tube K toward the right of the center line of the screen S, it will be seen that as this screen is scanned toward the right and reaches its ultimate right-hand position the horizontal sweep should he suddenly reversed and the commutator 21-28 suddenly reverses this saw-tooth voltage and causes the next sweep to extend from the point 0 to the extreme left-hand lower part of the screen S. In other words, by looking at the screen ,8 of the cathoderay tube K the saw-tooth voltages sweep the electron beam toward the left and back to the point 0 successively in reduced value whereas the voltages which sweep vertically gradually increase so that the net result will be a diagonal sweep. That is, when the vertical voltage is a maximum the left-hand sweep voltage becomes 0 so that various slanting radial scan lines, like the spokes of a wheel, are produced on the screen as conventionally illustrated by dotted lines 41 to 53, inclusive, on the screen S.

In the normal position of the apparatus as shown in Fig. 1A the electron beam is scanned vertically upward very quickly and downwardly almost instantaneously along the line 50. As now the shaft 23 in Fig. l is turned in a counterclockwise direction the voltages applied to the vertical plates l2 and I3 are gradually reduced and the voltages applied to the horizontal plates l0 and II are gradually increased in a positive direction so that various slanting lines of scan 7 conventionally illustrated by the dotted lines II, 52 and it until the first quarter turn of rotation of the rotor 2I--2 2 has been completed. At this point, end of first quarter turn, commutation takes place so that the voltage applied to horizontal plates II and II, which is now a maximum, is suddenly reversed causing'the electron beam to sweep to the left from the point instead of sweeping to the right and so that the sawtooth voltage applied to the sweep plates I2 and I3 again build up positively to cause theflrst half of a second sweeping of the screen S of the cathode-ray tube K to take place. In other words. the fluorescent'screen S of 'the cathoderay tube K is scanned radially twice during each revolution of the shaft. This shaft 23 is c0nnected to the shaft 24 through the medium of reduction gears I45 and I46, whereas in the Figs.

2 and 3 constructions they are connected by oneto-one ratio gears I00 and IIII, and in the Fig. 4 construction are connected through the medium of gears I41 and I48. In this connection it should be noted that the gears I45 and I48 cause the shaft 24 to rotate twice as fast as the shaft 23,

Fig. 1A of the drawings has been provided to activate the grid G of the electron gun of cathode-ray tube K at the proper instant out on the sweep and also on the proper radial line 48 to 53, inclusive, and others. The proper radial line on which a fluorescent dot is to be placed is selected by rendering the tetrode tube T inactive, through the medium of its suppression grid SG, during all other radial scans except the particular scan corresponding to the location in the field then under consideration, and this is done by supplying negative energy to this suppression grid SG of this tetrode T. The particular distance out on such radial line at which such fluorescent dot is placed is determined through the medium of the control grid CG of this tetrode T and. depends on the distance the particular ground station is from the airplane. This tetrode includes the usual plate P, the usual cathode Ca,

control grid CG, suppression grid SG, a plate battery 3? and the usual plate transformer TrP.

The checking transformers TrC I and TrC2 are employed to determine when the volume controlled voltages applied to the primary windings 60 and SI of these respective transformers are in perfect phase and this is accomplished by having their secondary windings 62 and 63 connected in bucking relationship, as shown. to the amplifier-detector 65 'through the mediums of wires 66 and 61. In other words, zero energy is only delivered from the transformers TrCI and TrC2 to the amplifier 65 when the voltages applied'to the primary windings 60 and 6| of these transformers are in exact phase. Out-of-phase energy so applied to these transformers and in turn to the amplifier-detector 65 is in turn converted into rectified potential of negative polarity and applied to the suppressing grid SG of the tetrode T, so that this tetrode T is at all times tothesewindingstlandflareofthe same value. In this connection it maybe pointed out" that the receivers-RI and R2 suitablev volume control apparatus so that their output voltages are substantially. of identical magnitude. If it is now desired'to plot afluoreseent dot on the screen 8 at some other point when verticallyabovethepoiritOandduetoafleldlocation which is not directly ahead of the .airplaneitshifting the phase of one of the received radio beams (the beamreceived from receiver RI) so as to artificially bring it into phase with the' other radio beam at such time as the electron beam in the cathode-ray tube scans that area on the screen S corresponding to the actual area in the field where such ground station is located, and to apply these artificially synchronized energies to the primary windings of the transformers TrCI and TrC2. v I

Such phase shifting apparatus has been provided through the medium of a-rotary transformer including stationary coils II and II, movable coil I2, and slip rings 13 and I4. The movable coil I2 and the slip rings I3 and I4 are I supported by the shaft 24 heretofore described.

When it is desired to shift phase to greater .extents than 90 electrical degrees it is necessary to produce a rotating magnetic field, or a rotating electro-static field as for instance may be accomplishedby apparatus such as shown in Fig. I.

For this reason the stationarycoil II is provided flowing in the coil II to lead theimpressed voltage by substantially 45. In other words, the current flow in the coils III and II is displaced substantially 90 electrical degrees so that a rotating magnetic field is produced about the center of these coils I0 and II as .a result of which a voltage is induced in the movable coil I2 having a phase relationship with respect to the input voltage derived from the receiverRI dependent upon the rotated position of this rotatable coil I2. The coils II and 'II receive their.

energy over wires 51 and ill from receiver RI. The receiver R2 is connected to the primary winding iii of transformer TrC2 through the medium of wires 68 and 69. The coill2 is connected to the slip rings I3 and I4 through the medium of wires I5 and I6 and is in turnap plied to the primary winding 60 of the transtical field, the rotating magnetic field produced by these coils will rotate counterclockwise. Also,

since rotation of the shaft 24 is clockwise the frequency applied to the input winding of suppressed and the tube is at all times rendered inoperative so long as the voltages applied to the primary windings 60 and GI are out of phase.

the transformer TrCI is one cycle more than is the alternating current frequency applied to the primary winding ill of the transformer TrC2 for each revolution'of the shaft 24, so that if this shaft 24 rotates thirty-two revolutions per second, as would be true since the gear I is again as large as the pinion I46, the frequency of the energy applied to transformer TrCI'is 32 cycles per second more thanthe frequency of the current applied to the transformer T102.

' In other words, once during each revolution of the shaft 24 (twicefor each revolution of the shaft 23) a complete cycle of phase shift takes place between the current supplied to the primary windings of transformers TrCl and T102.

Since the maximum phase shift that can exist between the currents received by receivers RI and R2 is 360 it is readily seen that the phase shifting apparatus is back to its normal positionafter having modified one received current to all possible extents of out-of-phase condition that can exist, as a result of which a second phase shift cycle of compensation may be started immediately after an entire series of phase shift corrections have been completed.

' but if it leads 180 it is a manifestation that the ground location is at right angles to the center line of the airplane and to the right thereof. To display these manifestations on the screen it will be necessary for the phase shifting apparatus illustrated inthe lower part of Fig. 1A to subtract 180 of phase shift when the shaft 24.

is in a position where the electron beam EB sweeps toward the left from the point on screen S but is required to add 180 of phase shift to this current when the electron beam sweeps directly toward the right from the point 0 on the screen, corresponding but less pronounced phase shifts being made for intermediate points in the field and for intermediate radial lines on the fluorescent screen S of the cathode-ray tube K.

OperationFig. 1A.Let us first assume that the apparatus is operating and that the sawtooth modifier shown near the top of Fig. 1A and the phase shifter shown in the lower part of Fig. 1A are, during this operation, for at least a moment, assuming the position indicated in the drawing. Under this condition the saw-tooth voltage applied to the vertical sweep plates l2 and I3 is a maximum and the voltage applied to the horizontal sweep plates I0 and II of the cathode-ray tube K is zero as shown at arrow 83 (Fig. 5), so that sweeping of the electron beam EB over the dotted line 50 on screen S now takes place. At this time the airplane is pointing directly at the ground station Stal so that the ratio energies or space energies received therefrom by the receivers RI and R2 are in perfect phase. Out-of-phase energies may be received from other ground stations at this time.

Since the coil 12 now assumes a position so as not to modify the phase of the energy transmitted from the receiver RI to the primary winding 60 of the transformer TrCl the phases of the currents in primary windings 60 and 6| remain in phase and the voltages induced in the secondary windings 62 and 63 are in perfect bucking relationship so that zero voltage is applied to the amplifier-detector 65 and to the suppressing grid SG of the tetrode T. No suppression of operation of this tetrode due to this reception is therefore now effective and the tube may be caused to function by the application of poten- I tial to its control grid. Also, at this time, and

once for each sweep of the electron beam, voltage is supplied over wires 68 and III to the control grid CG of this tetrode 'I The tetrode T therefore functions at the proper instant and supplies high frequency energy to the grid G of the to the area covered, by the radial line 5| thephase corrections carried out by the phase shifting means shown in the lower part of Fig. 1 will not result in any reformed in-phase energies flowing in the primary windings 60 and 6| of the transformers TrCI and TrC2 when this line 5I is" being scanned," so that the suppressing grid SG of the tetrode T is continuously suppressing while the line 5| is being scanned by the electron beam. The amplifier-detector 65 is employed to produce a more or less continuous negative direct current suppressing voltage for the suppressing grid SG.

Let us now assume that the saw-tooth energy modifier shown in the top part of Fig. 1A and associated with shaft 23 has been rotated toward the left to an extent of substantially 45 to thereby cause scanning over radial line 52 on screen S. Under this condition medium saw-tooth voltages are applied to both sets of sweep plates III-II and I2-I3 of the cathode-ray tube K in that this apparatus now assumes the position as indicated by arrow in Fig. 5 of the drawings. The electron beam EB now sweeps over dotted line 52 illustrated on screen S. At this time radio energy picked up from station Sta2 reaches the receiver R2 substantially one-fourth cycle earlier than receiver RI. Since, however, the shaft 24 rotated a quarter of. a revolution as compared with an eighth of a revolution of shaft 23 the voltage'induced in rotatable coil 12 of the phase shifter has been advanced one-fourth of a cycle. In this connection it should be remembered that the direction of rotation of the magnetic field produced by stator coils I0 and II is counter-clockwise whereas the direction of rotation of shaft 24 and coil 12 is clockwise. In other words, the out-ofphase radio beams received by receivers RI and R2 from station Sta2 are converted into in-phase energies which energies are applied to the primary windings 60 and SI of the transformers TrCI and TrC2 respectively so that the voltages induced in their secondary coils are in perfect bucking relationship in their circuit and zero suppressing energy is applied to the amplifier-detector 65 to allow the control grid CG to function and plot the fluorescent dot 64 on radial line 52.

The in-comin cycles, which are intermittent by reason of the impulse generator IG, cause momentary activation of the control grid CG to thereby plot a fluorescent dot 64 on the screen S, there being no suppression, at the proper distance out on the dotted line 52 to not only show in what direction the station Sta2 is located but to also manifest the distance to such station.

Let us now assume that the apparatus continues to rotate and when it has rotated to an extent where the saw-tooth modifier shown in the upper part of Fig. 1A has rotated toward ll the left and the phase shifter in the lower portion has rotated one-half revolution toward the right. Under this condition the saw-tooth energies will be of values as indicated adjacent the arrow 45 in Fig. of the drawings, namely, the

I vertical plates will be energized by substantially zero saw-tooth voltage whereas the horizontal sweep plates will be energized by maximum voltage for sweeping the electron beam either toward the right or toward the left on the screen S depending upon whether pole changing by commutator 2'I28 has taken place. It willbe assumed'that there is no field station toward the extreme right or left of the center line 8| of the airplane shown in Fig. 1B of the drawings, so that the energies applied to the primary windings 60 and GI of the transformers TrCI and TrC2 received from other stations are due to this phase shifting out of phase and causes suppression of functioning of the tetrode T.

Let us now assume that the apparatus continues to operate and the shaft 23 turns-an additional 60 (60 change in radial scanning to radial dotted line 49) toward the left resulting in the turning of the shaft 24, 120 toward the right. Under this condition the saw-tooth voltages will be of a value as indicated by the arrow 82, so that the electron beam will sweep substantially over the radial. dot line 49 on the screen S. Under this condition the radio energy received by receiver RI from stat on Sta3 will leadthe radio energy received by receiver R2 by substantially one-sixth cycle or substantially 60 electrical degrees.

This one-sixth cycle may be verified from Fig. 1B of the drawings for if the ground station Sta3 now under consideration is substantially 30 toward the left of the dotted line 8|, 60 from the extreme left, as indicated by the dotted line 84, then the difference in the length of the lines 88 and 85, namely the distance from the point 86 to thereceiving antenna RA2, is substantially proportional to this 30 angle. This is not strictly true, in that the line 86-RA2 is not a segment of the periphery of a circle drawn about antenna RAI as a center but is substantially acord. It should be noted that since line 84 is displaced 30 .from line 8| and that line RAI-II6 is displaced substantially 30" from the line RA| RA2.

Since approximate correct plotting of stations on the screen S is all that is necessary it may for convenience be assumed that the line 86-RA2 is one-third the spacing of the receiving antennas RAI-RA2 so that the phase displacement of the currents is approximately 60. In other words, the electron beam EB sweeps over the dotted line 49 of screen S at a time when'the radio energy received by receiver RI from a correspondingly located ground station Staii is artificially caused to lead by the phase shifter ahead of the radio energy received by receiver R2 by substantially 300 which is equivalent to a lag of 60". That is, if the energy that is now picked up by antenna RAI actually leads the energy picked up by antenna RA2 by 60 then this phase shifter which now creates an artificial lead of 300 (lag of 60) will cause in-phase energies to be created and applied to the primary windings 60 and 6| of transformers TrCI-TrC2 to remove suppression and allow plotting of a fluorescent dot 54 on dotted line 49 of screen S. That is, the phase shifter assumes a position of clockwise rotation from the position illustrated in the drawings of 90+90+120 or 300, which is five-sixths of a rotation of the rotor I2, so that the phase shifter of which it comprises a part will advance the 2 u phase of the radio energy supplied to the prima winding 60 of the transformer TrCI to an extent of substantially 300 the equivalent of retarding the phase 60 which is the electrical phase dis- I placement between lines 4! and '00 (physical spacing is 30). Since the energy supplied to receiver RI from station Stat leads substantially .60 aheadof the energy received by receiver R2 from the same station. this phase shifting function causes the energies supplied to the primary windings and BI of the transformers TrCI and TrC2 to be in phase resulting in perfect bucking relationship of voltages in the circuit including secondary windings 02 and 03 and resulting, in

zero suppressing energy i the amplifier-detector and resulting in zero suppressing energy being supplied to the grid SG of tetrode T. This tetrode T therefore is rendered responsive to energy applied to its control grid co and when the radio form of the invention, only partially illustrated in Fig. 2 of the drawingsis identical to the form illustrated in Fig. 1A in so many respects that only a small portion of the apparatus has been illustrated. In fact, the apparatus of this form of the invention, many parts of which have been omitted because they are identical, is identical to that shown in Fig. 1A, except in three respects. First, the radio frequency has been reduced to half, assuming the same spacing between antennas RAI and RA2, so that these receiving antennas are spaced only one-fourth cycle apart instead of being spaced one-half cycle apart as was assumed in the Fig. 1A structure. All tuned units are, of course, correspondingly adjusted.

Second, instead of employing slip rings I3 and I4 (Fig. 1A) for the phase shifter a single commutator including commutator segments and II is employed, so that after phase shifting through has been completed pole changing takes place screen S is only a half-cycle and this takes place during a half revolution of the shaft 24 whereas in the Fig. 1A construction an entire revolution of the shaft 24 was necessary for making all the phase shift corrections that could be confronted during a single scan of the fluorescent screen 8.

Third, since the phase shift mechanism including the rotatable coil I2 of the Fig. 2 construction performs the entire phase shift modification during a single scan of the screen S, that is, during a half revolution, it is no longer necessary to operate the shaft 24 at twice the speed of the shaft 23 and these two shafts may operate at the same speed. For this reason instead of employing speed-up gears I45 and I4 (Fig. 1) onetone ratio gears I00 and I III are employed.

In this connection reference should be had to Fig. 6 of the drawings to observe how phase shifting and the use of commutator 90-9I causes outof-phase radio currents to be brought into phase when the electron beam EB of the cathode-ray on screen S has advanced somewhat beyond dotted line 53 almost-90 of artificial lead imposed on current from receiver RI is necessary to bring current into phase and this is done and the condition is indicated by arrows IGI, I63 and I05.

An instant later, as shown by arrows I61, I08 and I69 (Fig. 6), commutation takes place.

Scanning now starts-on the left half of the screen and just below dotted line 41. This condition is indicated by arrows I62, I64 and IE6 on Fig. 6. One-fourth of a turn of shaft 24 after commutation has taken place (arrows I61, I68 and I69) zero artificial phase shift again takes I place as indicated by arrows I60, I and I80 (Fig. 6). The phase shifter of Fig. 2 therefore makes two complete series of phase shift corrections during each revolution of shaft 24 for which reason no speed-up gearing is required and oneto-one ratio gears I00 and IOI are used. The graphs of Fig. 6 are exaggerated in certain respects in that many more cycles, than indicated,

of radio frequency current pass between two successive commutations.

It is believed unnecessary to consider the operation of the modification illustrated in Fig. 2 in that it is the same as that of Fig. 1A except that since the maximum phase displacement that can exist between the radio currents received by receivers RI and R2 is only a half-cycle (Fig. 2) instead of a whole cycle (Fig. 1A) the speed of the shaft 24 has been reduced in half and-two complete phase shift correction functions are performed by this shaft 24 for each revolution thereof, whereas in the Fig. 1A structure a complete phase shift function requires a. complete revolution of shaft 24. As already pointed out this is possible because the leads feeding the primary winding 60 of transformer TrCI are pole changed each time a phase correction of 180 has been completed. In other words, the phase shift apparatus of Fig. 2 of the drawings can make only a maximum phase correction of 180 and it makes two such corrections during each revolution of the shaft 24.

Fig. 3,structure and operation-Referring for a moment to Fi 1A of the drawings it is obvious that the phase shifter shown therein advances the phase of the current supplied to the primary winding 60 one whole cycle during each revolution of the shaft 24. If now two such phase shifters were employed one of which advances the phase of the energy in the winding 60 over that received by the receiver RI and a second phase shifter which retards the phase of the energy supplied to the primary winding 3| during each revolution of the shaft 24 then the rate of phase modification would be doubled and the speed ratio gears I45 and I 46 of Fig. 1 would no longer be required in that a one-to-one gear ratio could be employed. This exact modification of Fig. 1A is illustrated in Fig. 3 of the drawings.

It will be seen that the gears I45 and I46 have been replaced by one-to-one ratio gears I00 and IOI and that a second phase shift structure including stationary coils I02 and I03 energized through a condenser I04 and an inductance I05 respectively are provided. It will be seen that this condenser I04 and inductance I05 are included in inverse order as compared with the inductance I1 and condenser I9 shown. This causes the rotating magnetic field set up by stationary coils I02 and I03 to rotate in the reverse direction as that produced by the coils I0 and II of Fig. 1 and also included in Fig. 3. It is thus readily seen that since the shaft 24 rotates in a clockwise direction that the alternating current induced in coil I2 will be increased by one cycle for each revolution of the shaft 24 whereas thealternating current induced in the rotatable coil I08 is reduced by one cycle for each revolution of the shaft 24, the net result is that for each revolution of the shaft 24 the current in the primary winding 60 of the transformer TrCI passes the current supplied to the prim Winding 6| of the transformer TrCZ twice and for this reason the shaft 24 need only run half as fast in the Fig. 3 structure as it would in the Fig. 1A structure. In Fig. 3 the energy derived from the rotating coil I2 is conducted to the primary windin 60 of the transformer TrCI through slip rings I3 and I4 and wires H0 and H9 whereas the alternating current induced in the coil I02 is conducted to the primary winding 6| .of the transformer TrC2 through the medium of slip rings H0 and III and wires I28 and,l29. The operation of the system illustrated in- Fig. 3 in I all other respects is the same as that of the Fig.

tennas RAI and RA2 are spaced one-fourth cycle apart (onehalf in Fig. 3) so that the extent of phase shift which must be modified is limited to or a half cycle. In order to avoid loss of time in having the phase shift apparatus operate through a half cycle where phase shifts are made by the structure that can never be used it is proposed to employ a commutator so that only phase shifts through an extreme range of 180 will be corrected. This has been accomplished by providing a four-segment commutator II2-II5 of which the segments H2 and H4 are connected together to wire I I6 and of which segments H3 and H5 are connected together and to the coil I2 through the medium of wire II I. The brushe engaging this commutator are connected through two suitable wires H8 and H9 to the leads of the primary winding 60 of the transformer TrCI. It is thus seen that after each one-fourth revolution of the shaft 24 pole changing of the input leads of the transformer TrCI takes place so that since two cycles of correction are made through each revolution thi pole changing takes place after each 180 of phase shift modification.

For reasons already pointed out the shaft 24 is then required to operate only one-half as fast as does the shaft 24 of Fig. 3, for which reason step-down gearing comprising a driving pinion I4'I of half the diameter of the driven gear I48 has been provided so that the shaft 24 rotates half as fast as does the shaft 23. Stating this in different words, since four complete phase shift corrections take place in each revolution of the shaft 24 and since two complete scanning operations are performed during each revolution of the shaft 23 the shaft 24 need only operate at half the speed of the shaft 23. It is believed unnecessary to discuss the operation of the modi.. fied form of the invention illustrated in Fig. 4 in that it functions exactly the same as does the form of invntion illustrated in Fig. 3 except that maximum corrections of 180 are only required in the Fig. 4 structure whereas phase corrections extending through an entire cycle must be compensated for inthe Fig. 3 structure. For this reason the speed of shaft 24 may be reduced in half from that of Fig. 1A by reason of the fact that two phase shifting rotary transformers are employed in Fig. 4 instead of only one as shown in Fig. 1A and may again be halved by reason of the commutation performed so that the speed of the shaft 24 in the Fig. 4 structure is only onefourth that of the speed of the shaft 24 of the Fig. 1A structure.

Fig. 7 structure and operati n.-The phase shift compensators illustrated, in Figs. 1A, 2, 3 and 4 are phase shifters of the rotary transformer or inductive type in which a rotating magnetic field is established with which a rotatable coil may come into inductive relationship at various points in its rotation.

Fig. 7 illustrates a phase shifter for accomplishing similar functions in which a rotating electro-static field is established through the medium of four condenser plates I2I, I22, I23 and I24 which are fed by high potential secondary windings I26 and I21 of transformers Tr3 and Tr4. windings I26 and I21 of these transformers are displaced in phase substantially 90 so that the condenser plates I2I,- I22, I23 and I24 become positive successively in that order once for each cycle. A rotatable condenser plate I30 is provided so as to electro-statically conduct current i from these condenser plates 'I2l-I24 to the slip ringv I3I successively in overlapped relation. Since the electro -static rotating field produced by the condenser plates I2I-I24 rotates counterclockwise and since the shaft 24 rotates clockwise the energy delivered to the primary winding 66 of the transformer TrCI is advanced one en-' tire cycle over that of the current supplied to the primary windings of transformers T13 and Tr4 during each revolution of the shaft 24.

Since the phase shifting rate of the phase shifter illustrated in Fig. 7 is the same as that illustrated in Fig. 1A this electro-static phase shifter illustrated in Fig. 7 may be substituted for the inductive phase type shifter illustrated in Fig. 1A for obvious reasons. As pointed out hereinafter the voltages induced in the secondary windings I26 and I21 of the transformers Tr3 and T14 are displaced 90 in phase. It may be pointed out that this phase displacement is accomplished through the medium of the condenser I34 and the resistance I35 connected across the primary windings I36 and I31 of the transformers Tr3 and TM respectively.

It may be pointed out that these primary windings I36 and I31 are connected in series and that the current flowing in the winding I31 leads the current flowing in the winding I36 because the winding I36 is shunted by a condenser I34 and the winding I31 is shunted by a resistance I35. This condenser I34 is of such capacity and resistance I 35 is of such ohmic value that the phase The voltages induced in the secondary l6 displacement in the primary windings I33 and I31 is substantially 90 electrical degrees.

Since the functioning of the system is exactlyv thesame irrespective of whether inductive type phase shifters or electro-static type phase shift- I ers are employed no description of the operation of the system whensuch electro-static phase shifters are employed is believed'necessary and will therefore not be given. The one-to-one ratio gears illustrated in Figs. 2 and-3 will in practice I be preferably omitted'and a shaft coupling used I instead. These gears have been illustrated ;to avoid confusion relative to direction of rotation of the phase shifters.

Fig. 8 structure and operati0n.--In each of the forms of invention illustrated in Figs. 1. 2, 3 and 4 phase shifting of radio frequency currents was accomplished by electro-magnetic inductive phase shifting means whereas in the form illustrated in Fig. 7 this'was accomplished by a ro- -tatable phase shifter of the capacitance type.

There is still another principle whereby phase shifting to bring out-of-phase radio currents into phase and that is by varying the length of the conducting path of the received radio current.

It the length of the path were to be varied by changing the length of a conductor over which the current must flow the apparatus would become unduly cumbersome in view of the tremendousspeed of electric wave motion in a metallic conductor, and for this reason this method of changing the lengths of the conducting path is'impracticable. The speed of movement of the incoming radio energy is, however, tremendously reduced where this energy exists in the form of flow of electrons in space in anelectron tube.

Speaking generally, the velocity of an electron in an amplifier maybe as low as /1000 of the velocity of the radio wave in space which caused the electron flow. It is therefore proposed to provide means whereby each of the two received radio energies flow through variable length cath-' A structure of this type has been illustrated in I Fig. 8 wherein there have been illustrated two selector type amplifying: tubes STI and ST2.

Each of these tubes .comprises a cylindrical envelope or glass tube in which there are concentrically provided two semi-circular plates or anodes PSI and PS2. Eccentrically enclosed with respect to the center of the envelope ES and similarly eccentrically located with-respect to the axis of two plates PSI and PS2 there is provided a cylindrical cathode CS about which there is concentrically located a grid G8. The cathode CS is heated in the usual way as bya filament passing through the center thereof and the grid GS is of the usual screen construction. Ifpoten- 'tial is supplied between the plate'PSI and the cathode CS and this cathode CS is heated electrons will flow from the cathode OS to they plate with more or less uniform distribution. If, however, the grid- GS is biased negatively this electron flow will be reduced and if it is biased positively the electron flow from the cathode CS will increase.

. It is well understood that if an electron is pro- 17 netic field that this electron flow will be in a spiral trajectory or path the curvature of which.

tate about the axis of the cathode at a speed equal to or proportional to the speed of the shaft 23. This shaft 23 is used for scanning the electron beam in the cathode-ray tube Kin the same manner as in Fig. 1A.

In order to produce a rotating magnetic field a typical two-phase motor stator, preferably of the toothed type is provided, in the slots of which there is wound a two-pole two-phase winding DW of the usual distributed type construction so that if this winding is energized by two-phase alternating current the desired rotating magnetic field will be present. Three-phase or six-phase windings and corresponding sources of energy may of course be used. This cylindrical stator and distributed winding has been conventionally shown and has been designated DW. Since the selector tubes STI and ST2 are identical like parts have been assigned like reference characters. As shown the distributed windings DW are energized by two-phase alternating current from a two-phase alternating current generator 2PG. As shown in Fig. 8 the anode PS2 in each of the tubes STI and ST2 is not used and is merely provided to assist in carrying ofi the electrons which are projected toward this anode. This anode is preferably connected to the cathode CS through a suitable discharge resistance (not shown).

The two anodes PSI are supplied with current of positive polarity from the plate battery BPI, the selector tube STI having included in its plate circuit the primary winding 60 of the transformer TrCI whereas the selector tube ST2 has included in its plate circuit the primary winding 6| of the transformer TrC2. These transformers are part of the systems heretofore described. Also, the grid GS of the tube STI is connected to and at times activated by radio frequency current delivered by the receiver RI whereas the grid GS of the other tube ST2 is connected to and at times activated by energy delivered by the receiver R2. When the electron beams Eb cooperating with the anode PSI assumes the position illustrated in Fig. 8 the energy supplied from the receiver RI must flow over a much greater distance within the tube STI than does the energy supplied from the receiver R2 within the tube ST2. In other words, the transmitting distance through the tube STI is greater than average whereas the transmitting distance in the tube ST2 for this position of the electron beam is shorter than average, so that the current in the plate circuit of the selector tube STI has been caused to la whereas the plate current flowing in the plate circuit of the selector tube ST2 has been caused to'lead with respect to average. When, however, the shaft 23 assumes a position where the screen S 'of the cathode-ray tube K is being scanned vertically upwardly then the phases of the currents delivered by the two-phase generator 2PG are such as to cause polarity of the rotating magnetic field to be positioned and the electron beam Eb of the tube STI to assume the position I50 and the electron beam Eb of the tube ST2 to assume this phenomenon it is proposed to provide a units EDI and RD2.

the position I5I. It will be observed that the distances from the cathode CS to the plate PSI over paths I50 and I5I in tubes S'll and ST2 respectively are of equal length so that the currents passing therethrough have not been caused to either lead or lag in that such delay as was caused by both must be considered the normal and average condition. From this consideration it is readily seen that if the antennas RAI and RA2 are spaced one-half wave length apart so that the greatest displacement in phase that can ever exist is one whole cycle or 360 and that if the electron speed in these tubes is such that the diflerence between the longest and shortest electron beam Eb is one-half wave length that a whole wave length of shift in phase will be produced by each half revolution of the electron beam Eb. Since the shaft 23 causes the fluorescent screen S to be scanned twice in each revolution it is immediately apparent that no gear ratio between shaft 23 and shaft 24 is necessary and for this reason the shafts 23 and 24 have been illustrated coupled .together by a coupling I54.

Since the selector tubes STI and ST2 are to be used to amplify alternating current very little or no grid bias is preferably appliedto the grids GS so that the application of alternating current to these grids GS will result in sine wave fluctuations of the plate currents passing through the primary windings 6|] and GI of transformers TrCI and TrC2 so that strictly alternating currents flow in the secondary windings 62 and 63 respectively of these transformers.

Obviously the structure and operation of the system beyond the transformers TrCI and TrC2 is the same as that of the Fig. 1 construction for which reason it is deemed unnecessary to discuss the operation of the system any further.

Fig. 9 structure and operation.-Since the apparatus illustrated in Fig. 8, and just described, not only lends itself to produce phase shift in alternating currents but also lends itself to the measurement of difference of the time of arrival of two different pulses of radio energy the invention may take still a slightly different form and this has been illustrated in Fig. 9 of the drawings.

In the form of the invention, as illustrated in Fig. 9, the radio receivers RI and R2 have been shown replaced by radio receivers and detectors RBI and RD2, these receiver-detectors deliver rectified current instead of the alternating current from space radiation received through the medium of their associated receiving antennas RAI and RA2. In other words, direct currentpulses are dealt with beyond the receiver-detector Since the two selector tubes STI and ST2 are identical to the selector tubes illustrated in Fig. 8 these selector tubes as well as all of their component parts have been designated by like reference characters. From a complete understanding of the apparatus disclosed in Figs. 1A and 1B of the drawings and the operation of this Fig. 1A apparatus and from the fact that the receivers RI and R2 have been replaced by receiver-detectors EDI and RD2 in Fig. 9, it is obvious that the potentials applied to the grids GS of the tubes STI and ST2 of Fig. 9 will at times arrive simultaneously and will at other times arrive in sequence, depending upon whether the ground station ahead of the airplane is straight ahead or isto one side or the other of the center line of the airplane. It will also be understood that the control grid CG of the tube T will be energized by a positive pulse over wire I8 19 each time that a reflected radio pulse reaches the airplane carried antenna HA2. In order to at times prevent these pulses from being eflfective and at other times allow them to cause the flow oi current in the plate circuit of this tube T the suppression grid SG of this tube T is connected to the secondary windings 52 and 65 of the transformers T! and TrCI. This circuit includes the secondary windings 52 and 53 in bucking relationship, and a condenser I" which is shunted by a high resistance unit I51. This condenser I56 and resistance unit I51 have been provided to maintain or hold over the momentary pulse that will be created through the medium or the circuit including secondary windings 62 and II due to out-of-phase current supplied to the grids GS. The structure is such as to cause the pulse to be maintained at least as long as the received radio pulse lasts. In this connection it is proposed that the control grid CG ot the tetrode T will be'maintained active during the entire pulse of radio energy whereas the secondary windings 52 and 63 in series will deliver a voltage only during the non-overlapped portion of the two received rectified radio pulses and this hold-over, effected by'the condenser I55 and resistance unit I51, will cause the suppression grid SG to suppress received impulses that are non-synchronous and this suppression will continue throughout the entire overlapped portion of the received impulses, whereas if two impulses are simultaneously received (overlapping from the start) no net voltage will be delivered by the secondary windings 62 and 63 of transformers TrCl and T1'C2 in series so that no suppression of actuation of the tetrode T will take place.

Theoperation of this modified form of the invention beyond the tetrode T is exactly the same as that illustrated in Fig. 3, the coupling I54 having been provided in place of the one-toone gear ratio illustrated in Fig. 3 of the drawings, for which reason a detailed discussion of the operation of the form of invention illustrated in Fig. 9 is believed unnecessary and will be dispensed with.

The applicants have thus shown and described numerous forms of their invention. Insofar as Figs. 1-4 are concerned this has been done to get a more clear understanding of the principles underlying the invention rather than to show different species thereof. Figs. 7, 8 and 9 illustrate other forms of the invention employing generally the same principle of operation. In all the forms of the invention illustrated radial scanning of the fluorescent screen has been disclosed specifically but it should be understood that slow horizontal and fast vertical scanning such as disclosed in our prior application, Ser. No. 558,256, filed October 11, 1944, may be used, if desired. Other changes, modifications and adaptations of the invention may be made within the spirit and scope of the invention and so long as these changes come within the scope of the following claims.

What we claim as new is:

1. In a system of the type described; the combination with an airplane carried cathode-ray tube including an electron gun, a fluorescent screen and means for causing an electron stream emitted by said gun to scan said screen in a predetermined manner; a radio transmitting antenna on the ground and two radio receiving antennas on said airplane, said receiving antennas being located along a line substantially parallel to the transverse axis of the airplane betweenradio currents received from said transmitting antenna simultaneously by said receiving antennas depending on the part of said screen which is .then being scanned by said electron stream. a

2. In a system of the typedescribed; the combination with an airplane carried cathoderay' tube including van electron gun, a fluorescent screen and means for causing an electron stream emitted by said gun to scan said screen back and forth over successive radial lines emanating from a predetermined point on the screen; a radio transmitting antenna on the ground and tworadio receiving antennas on said airplane, said receiving antennas being located along a line substantially parallel to the transverse axis 01 the airplane and being separated a predetermined distance; and. means for causing said electron gun to be activated for predetermined phase displacements between radio currents simultaneously received-from said radio transmitting antenna by said receiving antennas depending on the radial line on said screen which is then being scanned by said electron stream.

3. In a system of the type described; the combination with an airplane carried cathode-ray tube including an electron gun, a fluorescent screen and means for causing an electron stream emitted by said gun to scan said screen in a predeterminedv manner; a radio transmitting antenna on the ground and two radio receiving antennas on said airplane, said receiving antennas being located along a line substantially parallel to the transverse axis .of the airplane and being separated a. predetermined distance; and means including phase shifting apparatus for causing said electron gun to be activated for predetermined phase displacements between radio currents simultaneously received by said receiving antennas .from said transmitting an-' tenna depending on the part of said screen which is then being scanned by said electron stream.

4. In a radio route delineating system for guiding pilots on airplanes; the combination with a transmitting antenna and two receiving antennas carried by an airplane, said receiving antennas being located along a line substantially parallel to the transverse axis of the airplaneand a predetermined distance apart; a ground located radio re-radiating station which when activated by radio energy of a particular frequency radiates radio energy of the same frequency, whereby it such re-radiated energy reaches the airplane from which it was transmitted from any other point than straight ahead phase displaced radio energy is received in said two receiving antennas; a cathode-ray tube on said airplane including an electron gun, a fluorescent screen and scan-, ningmeans for sweeping ,an electron stream emitted by said gun to scan said screen in a predetermined manner; an electronic tube including a control grid and a suppressing grid; suppressing mean for renderin said sup pressing grid active to thereby render said electronic tube inactive when out of phase radio energies are received by the respective receiving antennas; phase shifting means effective when rendering active to modify the phase of the radio energy received by one of said receiving antennas to match the phase of radio energy received by the other receiving antennas; means for rendering said control grid active each time radio enmeans effective 'to render said phase shifting means active and thereby permit said electronic tube to be active whenever the fluorescent screen in said cathode-ray tube is being scanned by its electron stream in an area on said screen corresponding to the location of the ground located re-radiating station from which such radio energies were transmitted.

5. In a radio route delineating system for guiding pilots on airplanes; the combination with a transmitting antenna and two receiving antennas carried by an airplane, said receiving antennas being located along a line substantially parallel to the transverse axis of the airplane and a predetermined distance apart; a ground located radio re-radiating station which when activated by radio energy of a particular frequency radiates radio energy of the same frequency, whereby it re-radiated energy which originates at such transmitting antenna reaches the receiving antennas on said airplane from any re-radiating station other than a station straight ahead phase displaced radio energies are received in said two receiving antennas; a cathoderay tube on said airplane including an electron gun, a fluorescent screen and means for sweeping an electron stream emitted by said gun to scan said screen radially with respect to a point on said screen; an electronic tube eifective when active to increase the intensity of said electron stream, said electronic tube including a control grid and a suppressing grid; suppressing means ror rendering said suppressing grid active to thereby render said electronic tube inactive when radio energies are received which are not in phase; phase shifting means for modifying the phase of the radio energy received by one of said receiving antennas; means for rendering inactive when only one of said two receiving antennas are activated at a time; modifying means for causing successively arrived'radio energies received by said receiving antennas to be brought into synchronism; means for rendering said control grid active each time radio energy is received by one or said receiving antennas; and means for coordinating said modifying means and said scanning means so that in-synchronism radio energies created by said modifying means are only supplied to result in inaction of said suppressing means while rendering said control grid active when the fluorescent screen in said cathode-ray tube is being scanned by its electron stream in an area on saidscreen corresponding to the location of the ground located re-radiating station which emitted such radio energies.

7. A route delineating system for blind flying comprising; an airplane carried cathode-ray tube including a fluorescent screen, an electron gun and means for, causing said fluorescent screen to be scanned by an electron stream emitted from said gun over radial lines all starting at a common point each scan moving out very quickly and returning almost instantly, a plurality of ground stations defining air routes, means for emitting a train of radio waves .toward said ground stations at the beginning of each radial line scan, means at each ground station for returning a corresponding train of waves back to the airplane, receiving means on the airplane ineluding spaced antennas for comparing therphase said control grid active each time radio energy is received-by one of said receiving antennas; and means governed by said scanning means efiective to render said phase shifting means active and thereby permit said electronic tube to be active whenever the fluorescent screen in said cathode-ray tube is being scanned by its electron stream over a radial line on said screen corresponding to the location of the ground located re-radiating station which emitted such radio energies.

6. In a radio route delineating system for guiding pilots on airplanes; the combination with a transmitting antenna and two receiving antennas carried by an airplane, said receiving antennas being located along a line substantially parallel to the transverse axis of the airplane and a predetermined distance apart; a ground located radio re-radiating station which when activated by radio energy of a particular frequency will radiate radio energy of a given frequency, whereby if such re-radiated energy reaches the airplane from which it was transmitted from any other point than straight ahead the two detected radio energies will be received in said two receiving antennas successively; a cathode-ray tube on said airplane including an electron gun, a fluorescent screen and means for sweeping an electron stream emitted by said gun to scan said screen in a predetermined manner; an electronic tube for governing the intensity of said electron stream, said electronic tube including a control grid and a suppressing grid; sup-- pressing means for rendering said suppressing grid active to thereby render said electronic tube of radio frequency waves received simultaneously by the respective antennas from each or the ground stations, and means on saidairplane responsive to said receiving means for plotting a fluorescent dot on a particular radial line by rendering said electron stream active only if there is an active ground station located in a corresponding radial direction ahead of the airplane.

8. A route delineating system for blind flying comprising; an airplane carried cathode-ray tube including a fluorescent screen, an electron gun and means for causing said fluorescent screen to be scanned by an electron stream emitted from said gun over-radial lines all starting at a common point each scan moving out very quickly and returning almost instantly, a plurality of ground stations defining air routes, means for emitting a train of radio waves toward said ground stations at the beginning of each radial line scan, means at each ground station for returning a corresponding train of waves back to the airplane, receiving means on the airplane including spaced antennas for comparing the phase of radio frequency waves received simultaneously by the respective antennas from each of the ground stations, and means on said airplane responsive to said receiving means for plotting a fluorescent dot on a particular radial line by rendering said electron stream active only if there is an active ground station located in a corresponding radial direction ahead of the airplane and plotting such dot on said radial line at a distance out from said common point commensurate with the distance from such airplane to such ground station.

9. In a system of the type described; the combination with an airplane carried cathode-ray tube including an electron gun, a fluorescent screen and means for causing an electron stream emitted by said gun to scan said screen in a predetermined manner; a radio transmitting antenna on the ground and two radio receiving antennas on said airplane, said receiving antennas being located along a line substantially parallel aware? 23 to the transverse axis or the airplane and being separated a predetermined distance; and means including phase shifting means for Selectively advancing or retarding the phase of the radio energy received by one of said receiving antennas in accordance with whether said transmitting antenna onthe ground'is to the left or right of the longitudinal axis otthe airplane for causing said electron gun to be activated for predetermined phase displacements between radio energies received by said receiving antennas depending on the part of said screen which is then being scanned by said electron gun.

10. A route delineating system for blind flying comprising; an airplane carried cathode-ray tube including a fluorescent screen, an electron gun and means for causing said fluorescent screen to be scanned by an electron stream emitted from said gun over radial lines all starting at a common point each scan moving out very quickly and returning almost instantly, a plurality of ground stations defining air routes, means on the airplane for emitting a train of radio waves toward said ground stations at the beginning of each radial line scan, means at each ground station for returning a corresponding train of waves back to the airplane, receiving means on the airplane including spaced antennas for comparing the phase of radio frequency waves received simul- REFERENCES crrnn The following references are oi record in'the file of this patent:

, UNITED STATES PATENTS Number Name 'Date 2,189,549 Hershberger Feb. 6, 1940 2,198,113 -Holmes Apr. 23, 1940 2,225,046 Hunter Dec. 17, 1940 2,226,860 Greig Dec. 31, 1940 2,231,929 Lyman .Feb. 18, .1941 2,241,809 Deforest May 13,-1941 2,312,761 Hershberger Mar. 2, 1943 2,313,966 Poch Mar. 16, 1943, 2,396,112 Morgan Mar. 5, 1946 2,403,562 Smith July 9, 1946 2,403,625 Wolff July 9. 1946 2,405,238 Seeley 'Aug. 6, 1946 2,420,408 Behn May 13, 1947 2,426,189 Espenschied Aug. 26, 1947 2,426,218 Hopgood- Aug. 26, 1947 2,427,219 Luck "Sept; 9, 1947 2,430,292 Hershberger Nov. 4, 1947 2,432,330 Norgaard Dec. 9, 1947 2,433,341

Busignies Dec. 30, 1947 

